Prevent map resizing in Write mode

### Description:

In [Write mode](https://github.com/WordPress/gutenberg/issues/60021), users should not be able to drag to resize the map. The map should maintain a fixed size to ensure focus on writing and prevent accidental resizing.

Steps to Reproduce:
1. Enter Write mode (ensure the Gutenberg experiment is active.
2. Attempt to drag the edges of the map to resize it.
3. Observe that the map’s resize handle is visible.

### Expected:

The map remains fixed in size and the resize handle is not available.

### Actual:

You can attempt to resize its edges in Write mode.

### Visual:

https://github.com/user-attachments/assets/dc6e250b-4541-44f6-8ac0-f393edfe0615

Reproduce the issue by enabling the Gutenberg experiment, entering Write mode, and dragging the map edges. Trace the map behavior from the Write mode entry point; done means the map stays fixed and its resize handle is unavailable in that mode.

Written by the indexing model from the issue text.